1. Field of the Invention
The invention relates to a measurement device and a measurement method for obtaining images of an object, such as functional images and morphologic images, by virtue of various magnetic resonances such as electron spin resonance (ESR) and nuclear magnetic resonance (NMR).
2. Description of the Related Art
Redox metabolism containing active oxygen and free radicals is much concerned with a lot of physiological phenomena, and causes and development of diseases. Accordingly, if redox dynamics in a laboratory animal could be visualized at an individual level, it would be possible without doubt to contribute to elucidation of life phenomenon, analysis of diseases, establishment of curing diseases, and development of medicines.
Electron spin resonance imaging (ESRI), in accordance with which free radicals as intermediate products of redox metabolism are peculiarly detected, is useful for visualizing redox dynamics. However, images resulted from ESRI lack correspondence with internal organs. In order to solve this problem, there has been developed an ESRI-MRI combination type apparatus for analyzing magnetic resonance images, in which images resulted from ESRI are superimposed with MRI images of internal organs obtained by magnetic resonance imaging (MRI).
Overhauser effect is a phenomenon in which electron spin of free radicals is made to be ESR-transited to thereby cause nuclear spin to be polarized by virtue of dipole-dipole interaction between electron spin and nuclear spin. OMRI is an imaging process in which after electron spin of free radicals is excited, hydrogen nuclear spin of water molecule is polarized for carrying out MRI measurement. In OMRI, nuclear spin polarization is 330-times intensified at maximum (theoretical value) in comparison with Boltzmann distribution of usual nuclear spin. That is, OMRI makes it possible to realize 330-times sensitization (theoretical value) in comparison with usual MRI measurement.
The inventors of the present application suggested, in Japanese Patent Application Publication No. 2006-204551, the measurement device for obtaining images of organism structures by virtue of various magnetic resonances such as electron spin resonance and nuclear magnetic resonance. The measurement device is designed to include means for generating a first magnetic field having a certain intensity, means for generating a second magnetic field having an intensity greater than the intensity of the first magnetic field, means for linearly moving an object between the first magnetic field generating means and the second magnetic field generating means in synchronization with irradiation of RF pulses onto the object, and means for stopping the object to move, and obtaining images of organism structure of the object in accordance with signals detected in response to the RF pulses.
In the above-mentioned measurement device, the means for generating a first magnetic field may be employed as both an apparatus for generating an external magnetic field for ESRI and an apparatus for exciting electron spin for PEDRI (OMRI), and the means for generating a second magnetic field may be employed as an apparatus for generating an external magnetic field for MRI and OMRI. Thus, images of an amount of radicals varying with the lapse of time are obtained by OMRI, and images of radicals varying in quality are obtained by spectrum/spatial four-dimensional ESRI/MRI, and further, a magnetic field generated by the means for generating a second magnetic field can be designed to have a high intensity, resulting in that it is possible to obtain images having high sensitivity and high resolution.
In the above-mentioned measurement device, the means for linearly moving an object, disposed between the first magnetic field generating means and the second magnetic field generating means, causes the object to reciprocatingly move, and after the object is caused to stop, the measurement is carried out. Thus, high acceleration is applied to the object when the object starts moving and is stopped. Consequently, the above-mentioned measurement device is accompanied with a problem that high load is unavoidably applied to the organism as the object while moving.
Thus, the inventors are presently developing a measurement device which is able to measure an object moving between a plurality of magnetic field generating means, without stopping the object to thereby avoid the object from being loaded. However, measuring an object without stopping the object, there newly arises a problem that images of the object are influenced by a moving velocity, and resultingly, images of the object are shifted.
In view of the above-mentioned problems, it is an object of the present invention to provide a measurement device and a measurement method for obtaining images of an object to be measured such as functional images and morphologic images by virtue of magnetic resonance, both of which are capable of providing accurate images by eliminating influences caused by a moving velocity to a moving object.
A measurement device for obtaining images of an object to be measured by virtue of magnetic resonance, in accordance with the present invention, includes a magnetic field generator for generating a magnetic field to excite magnetic resonance of the object, a mover for moving one of the object and the magnetic field generator to thereby move the object in a magnetic field generated by the magnetic field generator, a measurement unit for applying a gradient magnetic field in at least one of a moving direction “y” in which the object moves relative to the magnetic field generator, and a direction “x” perpendicular to the moving direction “y” to thereby obtain image signals of the object by virtue of at least one of phase-encoding and frequency-encoding without stopping the object or the magnetic field generator while they are being moved by the mover, and a correction unit for eliminating influence on the image signals derived from movement of the object in the moving direction “y” to provide corrected image signals.
A measurement method for obtaining images of an object to be measured by virtue of magnetic resonance, in accordance with the present invention, includes moving one of the object and magnetic field generator which generates a magnetic field to excite magnetic resonance of the object to thereby move the object through a magnetic field generated by the magnetic field generator, applying a gradient magnetic field in at least one of a moving direction “y” in which the object moves relative to the magnetic field generator, and a direction “x” perpendicular to the moving direction “y” to thereby obtain image signals of the object by virtue of at least one of phase-encoding and frequency-encoding without stopping the object or the magnetic field generator while they are being moved, and eliminating influence on the image signals derived from movement of the object in the moving direction “y” to provide corrected image signals.
In accordance with the above-mentioned invention, even if the object to be measured or the magnetic field generator were moving by the mover, it would be possible to obtain corrected image signals in which the influence on the image signals derived from movement of the object relative to the magnetic field generator in the moving direction “y” is eliminated, ensuring it possible to provide accurate non-shifted images of the object, such as functional images and morphologic images.
It is preferable that the corrected image signals are obtained in accordance with the following equation:
            S      ′        ⁡          (                        k          x                ,                  k          y                    )        =            exp      ⁡              [                              ⅈ                          2              ⁢              π                                ⁢          γ          ⁢                                          ⁢                      G            y                          (              n              )                                ⁢                      {                                                                                v                    y                                    2                                ⁢                Δ                ⁢                                                                  ⁢                                  t                  y                                            +                                                v                  y                                ⁢                                  t                                      y                    ⁢                                                                                  ⁢                    0                                                                        }                    ⁢          Δ          ⁢                                          ⁢                      t            y                          ]              ⁢          S      ⁡              (                              k            x                    ,                      k            y                          )            
wherein
S (kx, ky) indicates the image signals,
S′ (kx, ky) indicates the corrected image signals,
each of kx and ky indicates a spatial frequency in the directions “x” and “y” respectively,
“γ” indicates a gyromagnetic ratio, “Gy(n)” indicates an intensity of a gradient magnetic field of the phase-encoding or the frequency-encoding in n-th measurement,
“vy” indicates a moving velocity in the moving direction “y”,
“Δty” indicates a period of time during which the phase-encoding or the frequency-encoding is applied, and
“ty0” indicates a period of time until the phase-encoding or the frequency-encoding starts being applied.
Thus, it is possible to obtain the corrected image signals S′ (kx, ky) in which the influence on the image signals derived from movement of the object in the moving direction “y”, caused by a moving velocity in the moving direction “y”, a period of time during which the phase-encoding or the frequency-encoding is applied, and/or a period of time until the phase-encoding or the frequency-encoding starts being applied, is eliminated, ensuring it possible to obtain accurate non-shifted images of the object, such as functional images and morphologic images, in particular, accurate two-dimensional images.
It is preferable that the corrected image signals are obtained in accordance with the following equation:
            S      ′        ⁡          (                        k          x                ,                  k          y                ,                  k          z                    )        =            exp      ⁡              [                              ⅈ                          2              ⁢              π                                ⁢          γ          ⁢                                          ⁢                      G            y                          (              n              )                                ⁢                      {                                                                                v                    y                                    2                                ⁢                Δ                ⁢                                                                  ⁢                                  t                  y                                            +                                                v                  y                                ⁢                                  t                                      y                    ⁢                                                                                  ⁢                    0                                                                        }                    ⁢          Δ          ⁢                                          ⁢                      t            y                          ]              ⁢          S      ⁡              (                              k            x                    ,                      k            y                    ,                      k            z                          )            
wherein
S (kx, ky, kz) indicates the image signals,
S′ (kx, ky, kz) indicates the corrected image signals,
each of kx, ky and kz indicates a spatial frequency in the direction “x”, the direction “y”, and a direction “z”, respectively,
“γ” indicates a gyromagnetic ratio,
“Gy(n)” indicates an intensity of a gradient magnetic field of the phase-encoding or the frequency-encoding in n-th measurement,
“vy” indicates a moving velocity in the moving direction “y”,
“Δty” indicates a period of time during which the phase-encoding or the frequency-encoding is applied, and
“ty0” indicates a period of time until the phase-encoding or the frequency-encoding starts being applied.
Thus, it is possible to obtain the corrected image signals S′ (kx, ky, kz) in which the influence on the image signals derived from movement of the object in the moving direction “y”, caused by a moving velocity in the moving direction “y”, a period of time during which the phase-encoding or the frequency-encoding is applied, and/or a period of time until the phase-encoding or the frequency-encoding starts being applied, is eliminated, ensuring it possible to obtain accurate non-shifted images of the object, such as functional images and morphologic images, in particular, accurate three-dimensional images.
It is preferable that the magnetic field generator includes a first magnetic field generator for generating a first magnetic field having a predetermined intensity, and a second magnetic field generator for generating a second magnetic field having an intensity different from the intensity of the first magnetic field generator, and that the mover moves one of the object, the first magnetic field generator, and the second magnetic field generator to thereby move the object through magnetic fields generated by the first magnetic field generator and the second magnetic field generator in this order.
Thus, it is possible to obtain accurate non-shifted images of the object, such as functional images and morphologic images, by virtue of various magnetic resonances such as electron spin resonance and nuclear magnetic resonance, by causing a plurality of magnetic field generators to generate magnetic fields having intensities different from one another, and causing the object to pass in succession through the magnetic fields generated by the plurality of magnetic field generators.
It is preferable that the mover comprises rotating means a rotator which rotates one of the object and the first and second magnetic field generators to thereby move the object through magnetic fields generated by the first magnetic field generator and the second magnetic field generator in this order.
Thus, it is possible to obtain accurate non-shifted images of the object, such as functional images and morphologic images, by virtue of various magnetic resonances such as electron spin resonance and nuclear magnetic resonance, by causing the object or the first and second magnetic field generators to rotate, and causing the object to pass in succession through the magnetic fields generated by the plurality of magnetic field generators.
As an object to be measured in the present invention, there may be selected a body of a living (organism) or a material other than a living (for instance, semiconductor). When a living is selected as an object, there can be obtained accurate non-shifted images, such as redox dynamics images as functional images, organism functional image including metabolism images, and structural images (for instance, 13C, 1H, 31P nuclei) as morphologic images. When a material is selected as an object, there can be obtained accurate images such as morphologic images of structures and defects, and distribution images of a compound.
It is preferable that one of the first and second magnetic field generators excites nuclear magnetic resonance for measurement, and the other excites electron spin resonance for measurement, for instance, in order to obtain images of redox dynamics. Thus, it is possible to obtain accurate non-shifted images of redox dynamics of organism by virtue of OMRI.
Any one of the first and second magnetic field generators may generate a magnetic field having a higher intensity than the other. If the second magnetic field generator is designed to generate a magnetic field having an intensity higher than the same generated by the first magnetic field generator, the first magnetic field generator generating a magnetic field having a lower intensity may be employed as an apparatus for exciting electron spin for carrying out OMRI, and the second magnetic field generator generating a magnetic field having a higher intensity may be employed as an apparatus for generating an external magnetic field for carrying out MRI and OMRI. Thus, the second magnetic field generator provides MRI images and OMRI images. In particular, in the measurement device in accordance with the present invention, since electron spin is excited by the first magnetic field generator generating a magnetic field having a lower intensity, and thereafter, OMRI measurement is carried out by the second magnetic field generator generating a magnetic field having a higher intensity, an external magnetic field used for carrying out OMRI has an extremely high intensity, and hence, it is possible to obtain accurate non-shifted OMRI images having high sensitivity and high resolution.
On the other hand, if the first magnetic field generator is designed to generate a magnetic field having an intensity higher than the same generated by the second magnetic field generator, the first magnetic field generator generating a magnetic field having a higher intensity may be employed as an apparatus for generating an external magnetic field for carrying out MRI, and the second magnetic field generator generating a magnetic field having a lower intensity may be employed as an apparatus for generating an external magnetic field for carrying out OMRI. Thus, the first magnetic field generator provides MRI images, and the second magnetic field generator provides OMRI images.
As mentioned above, since the first or second magnetic field generator excites magnetic resonance for measuring an object in the measurement device in accordance with the present invention, it is possible to obtain accurate non-shifted images of an object such as functional images and morphologic images, by virtue of various magnetic resonances such as electron spin resonance and nuclear magnetic resonance.
The present invention provides the following advantages.
(1) In accordance with the present invention, by moving an object or magnetic field generator which generates a magnetic field for exciting a magnetic resonance of the object, the object is caused to move through a magnetic field generated by the magnetic field generator, and further by applying a gradient magnetic field in a moving direction “y” in which the object moves relative to the magnetic field generator or in a direction “x” perpendicular to the moving direction “y” to thereby obtain image signals of the object by virtue of phase-encoding and/or frequency encoding without stopping the object or the magnetic field generator while they are being moved. Eliminating the influence onto the image signals caused by the movement in the direction “y” out of the thus obtained image signals, corrected image signals can be obtained. Thus, even if the object to be measured or the magnetic field generator were moving by the mover, it would be possible to obtain accurate non-shifted images of the object, such as functional images and morphologic images, in which the influence caused by a moving velocity of the moving object is eliminated.
(2) By obtaining the corrected image signals in accordance with the following equation:
            S      ′        ⁡          (                        k          x                ,                  k          y                    )        =            exp      ⁡              [                              ⅈ                          2              ⁢              π                                ⁢          γ          ⁢                                          ⁢                      G            y                          (              n              )                                ⁢                      {                                                                                v                    y                                    2                                ⁢                Δ                ⁢                                                                  ⁢                                  t                  y                                            +                                                v                  y                                ⁢                                  t                                      y                    ⁢                                                                                  ⁢                    0                                                                        }                    ⁢          Δ          ⁢                                          ⁢                      t            y                          ]              ⁢          S      ⁡              (                              k            x                    ,                      k            y                          )            it is possible to obtain accurate non-shifted images of the object, such as functional images and morphologic images, in particular, accurate two-dimensional images, in which the influence on the image signals derived from the movement of the object in the moving direction “y”, caused by a moving velocity in the moving direction “y”, a period of time during which the phase-encoding or the frequency-encoding is applied, and/or a period of time until the phase-encoding or the frequency-encoding starts being applied, is eliminated.
(3) By obtaining the corrected image signals in accordance with the following equation:
            S      ′        ⁡          (                        k          x                ,                  k          y                ,                  k          z                    )        =            exp      ⁡              [                              ⅈ                          2              ⁢              π                                ⁢          γ          ⁢                                          ⁢                      G            y                          (              n              )                                ⁢                      {                                                                                v                    y                                    2                                ⁢                Δ                ⁢                                                                  ⁢                                  t                  y                                            +                                                v                  y                                ⁢                                  t                                      y                    ⁢                                                                                  ⁢                    0                                                                        }                    ⁢          Δ          ⁢                                          ⁢                      t            y                          ]              ⁢          S      ⁡              (                              k            x                    ,                      k            y                    ,                      k            z                          )            it is possible to obtain accurate non-shifted images of the object, such as functional images and morphologic images, in particular, accurate three-dimensional images, in which the influence on the image signals derived from the movement of the object in the moving direction “y”, caused by a moving velocity in the moving direction “y”, a period of time during which the phase-encoding or the frequency-encoding is applied, and/or a period of time until the phase-encoding or the frequency-encoding starts being applied, is eliminated.
(4) By designing the magnetic field generator to include a first magnetic field generator for generating a first magnetic field having a predetermined intensity, and a second magnetic field generator for generating a second magnetic field having an intensity different from the intensity of the first magnetic field generator, and further by designing the mover to move the object or the first and second magnetic field generators to thereby move the object through magnetic fields generated by the first and second magnetic field generators in this order, it is possible to obtain, without stopping the object to move, accurate non-shifted images of the object, such as functional images and morphologic images, by virtue of various magnetic resonances such as electron spin resonance and nuclear magnetic resonance.
(5) By designing the mover to comprise a rotator which rotates one of the object and the first and second magnetic field generators to thereby move the object through magnetic fields generated by the first magnetic field generator and the second magnetic field generator in this order, it is no longer necessary to reciprocatingly move the object, and it is possible to obtain accurate non-shifted images of the object, such as functional images and morphologic images, by virtue of various magnetic resonances such as electron spin resonance and nuclear magnetic resonance, without stopping the object or the first and second magnetic field generators and further with the object being moved in rotation. Thus, it is possible to eliminate a load exerted on the object, caused when the object is temporarily stopped in reciprocal movement during measurement carried out in a conventional manner, and further, possible to avoid the first and second magnetic field generators from being loaded when they are caused to stop.
(6) By designing one of the first and second magnetic field generators to excite nuclear magnetic resonance, and the other to excite electron spin resonance, it is possible to obtain accurate non-shifted redox dynamics images of organism by virtue of OMRI.
(7) If the second magnetic field generator is designed to generate a magnetic field having an intensity higher than the same generated by the first magnetic field generator, the first magnetic field generator generating a magnetic field having a lower intensity may be employed as an apparatus for exciting electron spin for carrying out OMRI, and the second magnetic field generator generating a magnetic field having a higher intensity may be employed as an apparatus for generating an external magnetic field for carrying out MRI and OMRI. Thus, an external magnetic field used for carrying out OMRI has an extremely high intensity, and hence, it is possible to obtain accurate non-shifted OMRI images having high sensitivity and high resolution.
(8) If the first magnetic field generator is designed to generate a magnetic field having an intensity higher than the same generated by the second magnetic field generator, the first magnetic field generator generating a magnetic field having a higher intensity may be employed as an apparatus for generating an external magnetic field for carrying out MRI, and the second magnetic field generator generating a magnetic field having a lower intensity may be employed as an apparatus for generating an external magnetic field for carrying out OMRI. Thus, it is possible to obtain accurate non-shifted OMRI images having high sensitivity.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.